Developmental neuroscience and psychopathology is a rapidly growing domain with established success and great potential to inform the understanding of the causal pathways and mechanisms of mental illness. This T32, which is focused on this domain, is co-led by Drs. Luby and Barch (with complimentary expertise in developmental psychopathology and neuroscience), and has been very successful in the first cycle of funding, enjoying a highly competitive national applicant pool and successfully launching all of the young scientists who have completed the program thus far. We seek to renew and expand this training grant, adding new expertise in a wider range of neuroimaging measures, as well as new faculty mentors with expertise in the neural effects of the gut microbiome. From a public health perspective, an infusion of new research scientists in the area of developmental neuroscience and psychopathology is a high priority. The proposed multi-disciplinary training approach is guided by a conceptual model that examines emotional, cognitive, behavioral, neurobiological and genetic and environmental aspects of psychopathology from a developmental perspective. Further, this training program is guided by a perspective that recognizes that the risk, onset, and course of psychiatric disorders arises through a complex interplay of brain developmental processes influenced by psychosocial, genetic, and biological (including gut microbial) factors that interact beginning in utero and continue throughout development. Numerous investigators at Washington University in St. Louis (WUSTL) have a rich track record of experience in many aspects of child neuroimaging and related methods, including a focus on structural and functional magnetic resonance approaches in very early childhood, evoked response potentials (ERP) and high density diffuse optical tomography (HD-DOT). Further, WUSTL has an international reputation in psychiatric genetics and gut microbiome work, with many investigators who can bring both behavioral and molecular genetic approaches to bear on understanding the neurobiology of developmental psychopathology. The program mentors have a rich body of available databases derived from longitudinal studies, several of which began in early childhood and in utero. The program mentors provide a unique multidisciplinary training environment in which to pursue this exciting domain focused on childhood, given the established collaborations between child researchers in the WUSTL School of Medicine clinical and basic departments, and the state of the program in neuroscience and neuroimaging at WUSTL that has been at the forefront of developmental cognitive and affective neuroscience. Further, interactions between researchers in basic and clinical developmental neuroscience offer an ongoing opportunity to help train the next generation of young scientists who can pursue questions about the developmental etiology of psychopathology from the perspective of core psychological and neural mechanisms of human behavior that can inform and span traditional boundaries of psychopathology, an approach central to the NIMH Research Domain Criteria Initiative (RDOC).